The present invention relates to the production of chloroprene-2 (2-chlorobutadiene-1,3) from 3,4-dichlorobutene-1 by reaction with an alkali metal hydroxide.
A method for producing chloroprene in an aqueous solution of an alkali metal hydroxide is described in U.S. Pat. No. 2,430,016. However, in practicing the aqueous process, the product distribution is not always satisfactory and the reaction time is long. The product distribution, i.e., production of acetaldehyde and 1-chlorobutadiene is excessive, causes, in part, lower yields of desired product. Operation of this process is undesirable because the problem of producing a brine solution free of organic compounds, particularly aldol condensation products and hydrolysis substitution products, is difficult. In order to eliminate these problems, it has been attempted to produce chloroprene in an anhydrous system, particularly alcoholic alkalis, as described in U.S. Pat. No. 2,180,115. While acetaldehyde and 1-chlorobutadiene production is reduced, insoluble solids, particularly sodium chloride, are produced from the reaction, and recovery of the product and solvent is difficult.
Alcohols have also been added to reaction systems in small amounts as catalysts for the reaction with the alkali metal hydroxide (see U.K. Pat. No. 1,218,869). The alcohol was disclosed in the patent as acting as a transfer agent to bring the feed into the aqueous phase to contact the alkali metal hydroxide. While rates and product distribution were improved, however, it was necessary to maintain caustic concentration at above 25%, resulting in disadvantages of the process. The use of a hydrocarbon such as xylene as the reaction medium is disclosed in U.S. Pat. No. 3,026,360, but no improvement in product distribution results and the reaction is retarded.
Homogenous solutions of brine and ether-alcohols are described in U.S. Pat. No. 3,079,446 wherein the reaction takes place in a solution of an ether-alcohol in the brine. The reaction system of said U.S. Pat. No. 3,079,446 is described as having from 10% to 50% by volume ether-alcohol solvent with respect to the volume of water present, resulting in a reaction system having a maximum of 33% an ether alcohol or water soluble cyclic ether. Although some improvement results, as with the other prior methods for producing chloroprene, this method also is fraught with difficulties and undesirable side reactions result. It is particularly true with respect to contamination of the brine to be disposed of.
Previously, experimenters, even those who employed alcohols in the reaction system, turned their attention to the reaction occurring in an aqueous system. Surprisingly, I have discovered that the practice of my invention gives the advantages these experimenters have been searching for. Yet it is my invention to use a two-phase reaction system wherein substantially all of the reaction occurs in the organic phase. Heretofore, this had not been done.